Co2 recovery system and method of recovering co2

ABSTRACT

A CO2 recovery system includes: a CO2 absorber that transports flue gas with CO2 into contact with a CO2 absorbent to remove the CO2 and discharges a rich solution that has absorbed the CO2; an absorbent regenerator that separates the CO2 from the rich solution to regenerate the CO2 absorbent as a lean solution; a gas discharge line where a CO2 entrained gas from the absorbent regenerator is discharged; a reflux water drum that produces reflux water by separating CO2 and water from the CO2 entrained gas; a separation-gas discharge line where the separated CO2 is discharged; a compressor that compresses the separated CO2 gas; a condensate water drum that forms compressor condensate water by separating water from the compressed CO2 gas to form compressor condensate water; and a compressor-condensate water line that supplies the compressor condensate water as in-system or out-of-system supply water.

TECHNICAL FIELD

The present invention relates to a CO₂ recovery system and a method ofrecovering CO₂ which are capable of efficiently using water within asystem.

BACKGROUND

In recent years, as one of the causes of a global warming phenomenon, agreenhouse effect caused by CO₂ has been pointed out, and there has beenan urgent need, internationally as well, to take measures to protect theglobal environment. The generation source of CO₂ extends over all fieldsof human activities that burn fossil fuel and the demand for itsemission reduction tends to be further intensified. Along with this, forpower generation facilities such as thermal power plants that use alarge amount of fossil fuel, a way of removing and recovering CO₂ offlue gas by bringing the flue gas of a boiler into contact with, forexample, amine-based CO₂ absorbent, and a way of storing the recoveredCO₂ without releasing it to the atmosphere have been actively studied.

As a method of removing and recovering CO₂ from the flue gas by usingCO₂ absorbent, there is employed a CO₂ recovery system that brings theflue gas into contact with the CO₂ absorbent in an absorber, heats up ina regenerator the absorbent that has absorbed CO₂ to separate CO₂ andregenerate the absorbent, and circulates the regenerated absorbent inthe absorber again for reusing. In this CO₂ recovery system, in terms ofmaintaining the water balance of the absorbent within the system, it isdesired that the supply of water from the outside of the system besuppressed to a minimum, by using water generated within the system asmuch as possible. Thus, it is conceived that a regenerator reflux deviceis installed to condense, as reflux water, water contained in emissiongas with which CO₂ discharged from the regenerator is entrained, and thereflux water is circulated and reused with, for example, a reclaimingdevice (Patent Literature 1: Japanese Patent Application Laid-open No.2012-166139).

However, according to the conception in Patent Literature 1, because thereflux water includes a slight amount of absorption component, it is notpossible to efficiently recover the absorption component in theoperation of reclaiming. In addition, the measures taken atnon-stationary time when the carry-over from the regenerator occurs insome operating conditions are not sufficient.

Furthermore, it is desired that compressor condensate water generated incompressing CO₂ in the flue gas discharged from the regenerator beeffectively used.

SUMMARY

According to one or more embodiments of the present invention, a CO₂recovery system includes a CO₂ absorber configured to bring flue gascontaining CO₂ into contact with a CO₂ absorbent to remove CO₂ from theflue gas, an absorbent regenerator configured to separate CO₂ from arich solution that has absorbed CO₂ to regenerate the CO₂ absorbent as alean solution, a gas discharge line to which a CO₂ entrained gasdischarged from a top of the absorbent regenerator is discharged, areflux water drum provided in the gas discharge line to separate waterin the CO₂ entrained gas as reflux water, a separation-gas dischargeline to which a CO₂ gas separated by the reflux water drum isdischarged, a compressor provided in the separation-gas discharge lineto compress the separated CO₂ gas, a condensate water drum provided inthe separation-gas discharge line to separate water in the separated CO₂gas as compressor condensate water, and a compressor-condensate waterline connected to the condensate water drum to supply the compressorcondensate water separated from the condensate water drum as in-systemsupply water or out-of-system supply water.

According to one or more embodiments of the present invention, a methodis of circulating and reusing with a CO₂ absorber a CO₂ absorbent forwhich CO₂ is removed by an absorbent regenerator. The CO₂ absorber isconfigured to bring flue gas containing CO₂ into contact with a CO₂absorbent to remove CO₂ from the flue gas. The absorbent regenerator isconfigured to separate CO₂ from a rich solution that is a CO₂ absorbenthaving absorbed CO₂ to regenerate the CO₂ absorbent as a lean solution.The method includes the steps of separating water in a CO₂ entrained gasdischarged from a top of the absorbent regenerator as reflux water,compressing a CO₂ gas separated by a reflux water drum, separating waterin the compressed CO₂ gas as compressor condensate water. The compressorcondensate water is used as in-system supply water or out-of-systemsupply water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a CO₂ recovery systemaccording to one or more embodiments;

FIG. 2 is a schematic diagram illustrating the CO₂ recovery systemaccording to one or more embodiments;

FIG. 3 is a schematic diagram illustrating the CO₂ recovery systemaccording to one or more embodiments;

FIG. 4 is a schematic diagram illustrating the CO₂ recovery systemaccording to one or more embodiments;

FIG. 5 is a schematic diagram illustrating the CO₂ recovery systemaccording to one or more embodiments;

FIG. 6 is a diagram illustrating a relation between the operating hours(h) of absorption-agent recovery operation and the absorption agentconcentration (wt %) of residual water in a reclaimer according to oneor more embodiments;

FIG. 7 is a schematic diagram illustrating a CO₂ recovery systemaccording to one or more embodiments; and

FIG. 8 is a schematic diagram illustrating a CO₂ recovery systemaccording to one or more embodiments.

DETAILED DESCRIPTION

The following describes embodiments of the present invention in detailwith reference to the accompanying drawings. The present invention,however, is not intended to be limited by the following exemplaryembodiments of the invention. The constituent elements in the followingembodiments include those that are easily assumed by a person skilled inthe art, that are substantially identical, and that are within a scopeof what is called equivalents. Moreover, the constituent elementsdisclosed in the following embodiments can be combined as appropriate.

The embodiments of the invention can effectively use, within a systemand outside the system, compressor condensate water for which the watercontained in compressed CO₂ that was generated in recovering CO₂ iscondensed.

When this compressor condensate water is used as reclaiming water in anabsorbent regeneration (reclaimer) process within the system, becausethe CO₂ absorbent component is hardly contained in the compressorcondensate water, the recovery efficiency of the CO₂ absorbent componentin a reclaiming residue in the reclaimer process is improved. When thecompressor condensate water is used in pump equipment within the system,it can be suitably used as pump seal water because of no impurities.

When the condenser compressed water is discharged and used outside thesystem, the reduction in the amount of emissions of entrained absorbent(entrained amine solution) entrained in emission gas discharged from aCO₂ absorber to the outside can be achieved, by lowering the dischargingtemperature of the emission gas for which CO₂ discharged from a top ofthe absorber has been removed and by retaining the water balance withinthe system.

FIG. 1 is a schematic diagram illustrating a CO₂ recovery systemaccording to one or more embodiments.

As illustrated in FIG. 1, a CO₂ recovery system 10A according to one ormore embodiments includes a flue gas cooling tower (hereinafter alsoreferred to as “cooling tower”) 16 that cools flue gas 11 containing CO₂discharged from, for example, a boiler, a gas turbine, and the like bycooling water 15, a CO₂ absorber (hereinafter also referred to as“absorber”) 18 including a CO₂ recovery unit 18A that removes CO₂ fromthe flue gas 11 by bringing (i.e., transporting) the flue gas 11containing the cooled CO₂ into contact with a CO₂ absorbent (hereinafteralso referred to as “absorbent”) 17 that absorbs CO₂, and an absorbentregenerator (hereinafter also referred to as “regenerator”) 20 thatregenerates the CO₂ absorbent 17 by releasing CO₂ from a CO₂ absorbent19 that has absorbed CO₂ (hereinafter also referred to as “richsolution”). Then, in this CO₂ recovery system 10A, the regeneratedabsorbent (hereinafter also referred to as “lean solution”) 17 for whichCO₂ has been removed by the absorbent regenerator 20 is sent to the CO₂absorber 18 and is circulated and reused as the CO₂ absorbent.

The cooling tower 16 is disposed on a gas supply line L₁ to which theflue gas 11 is supplied, and the cooling water 15 is circulated by apump 12 disposed on a cooling-water circulation line L₉. Then, afterbeing cooled by a cooler 13 that is disposed on the cooling-watercirculation line L₉, the cooling water 15 is supplied into the coolingtower 16 and cools the supplied flue gas 11 down to a certaintemperature.

The absorber 18 includes the CO₂ recovery unit 18A and a washing unit18B. The CO₂ recovery unit 18A removes CO₂ in the flue gas 11 by the CO₂absorbent 17. The flue gas 11 for which CO₂ has been removed is cleanedwith washing liquid 21 in the washing unit 18B placed on the upper sideon the downstream side of gas flow of the CO₂ recovery unit 18A. In thewashing unit 18B, the washing water 21 is circulated by a pump 36disposed on a washing-water circulation line L₇. Then, after beingcooled by a cooler 37 that is disposed on the washing-water circulationline L₇, the washing water 21 is supplied into the washing unit 18B andwashes the flue gas 11 that goes through and for which CO₂ has beenremoved while cooling it down to a certain temperature. At this time,the CO₂ absorbent entrained in the flue gas 11 is washed with thewashing liquid 21 and the CO₂ absorbent entrained in emission gas 11Adischarged to the outside is prevented from discharging, therebyachieving the reduction in emissions. The temperature of cooling theflue gas 11 is substantially identical to the supply temperature of theflue gas 11 in supplying it into the absorber 18, thereby maintainingthe water balance within the system. For example, when the water contentin the flue gas 11 that is supplied into the absorber 18 is 10 wt %, thecooling temperature is adjusted such that the water content of theemission gas 11A discharged from the top of the absorber 18 is also 10wt %.

In the absorber 18 and the regenerator 20, a rich-solution supply lineL₃ that discharges the rich solution from a bottom portion 18 a of theabsorber 18 and supplies the rich solution 19 toward the regenerator 20side and a lean-solution supply line L₄ that discharges the leansolution 17 from a bottom portion 20 b of the regenerator 20 andsupplies it toward the absorber 18 side are connected intersecting witheach other. At the intersection of the rich-solution supply line L₃ andthe lean-solution supply line L₄, a rich/lean-solution heat exchanger 25is disposed. In this rich/lean-solution heat exchanger 25, the richsolution 19 is heated by the lean solution 17 that is regenerated in theregenerator 20, and is supplied to the absorbent regenerator 20. Betweenthe rich/lean-solution heat exchanger 25 and the absorber 18, a leansolution pump 32 that raises the pressure of the lean solution 17 and alean solution cooler 33 that cools the lean solution 17 by cooling water(C.W) are disposed, and after being raised in pressure and cooled, thelean solution 17 is supplied into the CO₂ absorber 18.

On the bottom portion 20 b side of the regenerator 20, a reboiler 26disposed on a reboiler line L₅ is provided. In this reboiler 26, incirculating a part of the lean solution 17 in the reboiler line L₅, itis indirectly heated by saturated water vapor 27 and the water vapor issupplied to the inside of the regenerator 20. In the reboiler 26, asaturated-water vapor supply line L₆ that supplies the saturated watervapor 26 a is provided. On this saturated-water vapor supply line L₆, aseparation drum 26 b is disposed that separates vapor condensate water26 c.

As for the CO₂ recovery system 10A, there are a case in which it isretrofitted in order to recover CO₂ from an existing flue gas source anda case in which it is placed along a newly equipped flue gas source atthe same time. In the line of the flue gas 11, an openable and closeabledumper is installed, and is opened when the CO₂ recovery system 10A isin operation.

In the method of recovering CO₂ using this CO₂ recovery system 10A,first of all, the flue gas 11 containing CO₂ from a boiler, a gasturbine, and the like, for example, is sent to a flue gas cooling device16 after having raised the pressure by a flue gas blower (not depicted),and is cooled therein by the cooling water 15 and sent to the CO₂absorber 18.

In the CO₂ absorber 18, the flue gas 11 makes countercurrent contactwith the CO₂ absorbent 17 using an amine-based absorption agent, forexample. Then, the CO₂ in the flue gas 11 is absorbed in the CO₂absorbent 17 by chemical reaction. The CO₂-removed flue gas after havingremoved the CO₂ in the CO₂ recovery unit 18A makes gas-liquid contactwith the circulating washing water 21 containing the CO₂ absorbentsupplied from a nozzle in the water washing unit 18B in the CO₂ absorber18, and the CO₂ absorbent 17 entrained in the CO₂-removed flue gas isrecovered. Furthermore, the emission gas 11A for which the CO₂ has beenremoved is released outside the system by a gas discharge line L₂connected to the top portion. The rich solution 19 that has absorbed CO₂is raised in pressure by a rich solution pump 24 and, at therich/lean-solution heat exchanger 25, is heated by the lean solution 17that was regenerated by the absorbent regenerator 20 (the other of thelean solution 17 is cooled by the heat exchange) and is supplied to theabsorbent regenerator 20.

The rich solution 19 released to the inside from a lateral upper portion20 a side of the absorbent regenerator causes an endothermic reaction bythe water vapor supplied from the bottom portion 20 b side, therebydesorbing and releasing most of CO₂. The CO₂ absorbent that released inthe absorbent regenerator 20 a part or most of CO₂ is referred to assemi-lean solution. This semi-lean solution becomes, by the time itreaches the bottom portion 20 b of the absorbent regenerator 20, thelean solution 17 for which almost all CO₂ has been removed. As for thislean solution 17, a part thereof is heated up by the saturated watervapor 26 a in the reboiler 26 and supplies the water vapor for CO₂desorption to the inside of the absorbent regenerator 20.

Meanwhile, in a top portion 20 c of the absorbent regenerator 20, a gasdischarge line L₂₁ that discharges CO₂ entrained gas 28 entrained inwater vapor released from the rich solution 19 and the semi-leansolution in the regenerator, is connected. This gas discharge line L₂₁is provided with a cooler 29 that cools the CO₂ entrained gas 28entrained in water vapor and a reflux water drum 30 that flashes the CO₂entrained gas 28 after cooling for gas-liquid separation. Reflux water31 that has been separated and refluxed from the CO₂ entrained gas 28entrained in water vapor in the reflux water drum 30 is supplied by areflux-water circulation pump 35 disposed on a reflux water line L₂₃ tothe upper portion of the absorbent regenerator 20 and to the washingwater 21 side (*1).

At the top portion of the reflux water drum 30, a separation-gasdischarge line L₂₂ that discharges separated CO₂ gas 40 is connected.This separation-gas discharge line L₂₂ is provided with a compressor 41that compresses the CO₂ gas, a cooler 42 that cools the compressed gas,and a condensate water drum 44 that separates compressor condensatewater 43 for which water vapor is condensed by the compressor 41. CO₂gas 45 that was separated by the condensate water drum 44 is dischargedto the outside of the system via a gas discharge line L₂₄, is separatelycompressed by a compressor, and is recovered. This recovered CO₂ gas 45is injected into an oilfield by using enhanced oil recovery (EOR) or isreserved into an aquifer to achieve measures against global warming, forexample.

A plurality of compressors 41 may be placed, and in that case, there aremultiple compressors 41 and multiple condensate water drums 44, and aplurality of drums of compressor condensate water is obtained. In thefollowing description, according to one or more embodiments, a case inwhich a single compressor 41 and a single condensate water drum 44 areplaced will be explained.

At the bottom portion of the condensate water drum 44, acompressor-condensate water line L₃₀ that discharges the compressorcondensate water 43 is connected. To this compressor-condensate waterline L₃₀, connected are a first compressor-condensate water line L₃₁that supplies the compressor condensate water 43 as in-system supplywater 43A, a second compressor-condensate water line L₃₂ that suppliesthe compressor condensate water 43 as out-of-system supply water 43B,and a third compressor-condensate water line L₃₃ in which the distal endis connected to a reclaiming device 50 and that supplies the compressorcondensate water 43 as reclaiming water. Note that, first to thirdon-off valves V₁ to V₃ are disposed, respectively, in the first to thirdcompressor-condensate water lines L₃₁ to L₃₃.

The reclaiming device 50 is, for example, a pressurized reclaimingdevice and includes a reclaimer 51 that draws, as lean drawn liquid 17a, a part of the lean solution 17 to a branch line L₁₀ from thelean-solution supply line L₄ that supplies the lean solution 17regenerated in the regenerator 20. The reclaimer 51 also takes in andreserves the lean drawn liquid 17 a thus drawn liquid.

This reclaimer 51 is provided with an alkaline-agent supply unit 52 thatsupplies an alkaline agent 52 a to the inside via an alkaline supplyline L₁₁, a reflux-water supply line L₁₂ that supplies reflux water 31 ainside the reclaimer 51, the third compressor-condensate water line L₃₃that supplies the compressor condensate water 43, a recovery-steamdischarge line L₁₃ that supplies recovery steam 53 discharged from thereclaimer 51 into the bottom portion 20 b side of the regenerator 20,and a residue discharge line L₁₄ that discharges a reclaimer residue 54.Note that, in the branch line L₁₀, the alkaline supply line L₁₁, thereflux-water supply line L₁₂, the recovery-steam discharge line L₁₃, andthe residue discharge line L₁₄, fourth to eighth on-off valves V₄ to V₈,respectively, are disposed.

The reclaiming device 50 draws out the lean solution 17 from a branchportion of the lean-solution supply line L₄ before reaching therich/lean-solution heat exchanger 25 from the regenerator 20 via thebranch line L₁₀ as the lean drawn liquid 17 a and reserves it inside thereclaimer 51, heats it in a pressurized condition at high temperature(for example, 120 to 150° C.), and returns the absorption component,which was vaporized from the lean drawn liquid 17 a, to the bottomportion 20 b side of the regenerator 20 as the recovery steam 53, whiledischarging the reclaimer residue 54 that was enriched by heating.

The reclaiming device 50 mainly includes an absorbent reservoir and aheating unit. The absorbent reservoir is configured as the reclaimer 51of airtight vessel that reserves the lean drawn liquid 17 a. Thisheating unit is provided inside the reclaimer 51, and is made up of ahorizontal U-shaped steam pipe 55, a steam supply line L₁₅ that isconnected to one end of the steam pipe 55 and that supplies saturatedwater vapor 56 that is produced by being heated with a heat source (notdepicted) outside the reclaimer 51, and a condensate-water dischargeline L₁₆ that is connected to the other end of the steam pipe 55 anddischarges steam condensate water 57 to the outside of the reclaimer 51.

This reclaiming device 51 opens the fourth on-off valve V₄ and suppliesthe lean drawn liquid 17 a to the inside of the reclaimer 51, opens thefifth on-off valve V₅ and supplies the alkaline agent 52 a to the insideof the reclaimer 51 from the alkaline-agent supply unit 52, opens thethird on-off valve V₃ and the sixth on-off valve V₆ and supplies supplywater (the compressor condensate water 43 and the reflux water 31 a) tothe inside of the reclaimer 51, and lets the saturated water vapor 56 gothrough in the steam line L₁₅. Accordingly, the supplied lean drawnliquid 17 a and the supply water (the compressor condensate water 43 andthe reflux water 31 a) are heated to, for example, 120 to 150° C. byheat exchange in a non-contact manner. Then, deteriorated materials thatare non-volatile materials contained in the lean drawn liquid 17 aproduce salt with the alkaline agent 52 a to separate the salt from theabsorption component, and are enriched as the reclaimer residue 54 inthe reclaimer 51.

This reclaimer residue 54 includes liquid components (liquid componentsincluding the absorption component that was not recovered, the alkalineagent, and the supply water, and liquid components of non-volatilematerials) in the reclaimer 51, and solid components of non-volatilecomponents. This reclaimer residue 54 is discharged to the outside ofthe reclaimer 51 by opening the eighth on-off valve V₈. The dischargedreclaimer residue 54 is processed by incineration disposal or the like,for example.

Meanwhile, the water in the reclaimer 51 (the lean drawn liquid 17 a,the reflux water 31 a, and the compressor condensate water 43) isevaporated by the heating of the steam pipe 55. At this time, theamine-based absorbent that was freed by decomposition of the alkalineagent 52 a is vaporized by the heating. The recovery steam 53 in whichthis vaporized absorption component is entrained passes through theopened seventh on-off valve V₇ and, through the recovery-steam dischargeline L₁₃, is returned to the bottom portion 20 b side of the regenerator20 (*2). Accordingly, the deteriorated materials contained in the leandrawn liquid 17 a are separated, and a situation in which thedeteriorated materials are accumulated in the absorbent circulatinginside the system of the recovery system 10 can be prevented.

The principle of reclaiming of amine-based absorbent by using sodiumhydroxide as the alkaline agent will be described. By adding and mixingthe alkaline agent 52 a such as sodium hydroxide to the lean drawnliquid 17 a containing the absorption component (including aminenitrate, amine sulfate, and the like) that is fixed by the deterioratedmaterials and a part of impurities (including nitrate salt,hydrosulfate, and the like, for example), and by heating the mixture,the amine absorption component that became a free state is recoveredtogether with water as the recovery steam 53, and the non-volatilematerials (impurities, including sodium nitrate, sodium sulfate, and thelike) are separated and discharged to the outside of the system as thereclaimer residue (liquid and solid) 54.

The compressor condensate water 43 that is separated at thecompressor-condensate water line L₃₀ from the condensate water drum 44is, broadly speaking, divided into in-system supply water 43A suppliedby the first compressor-condensate water line L₃₁ that is the water usedwithin the system, and into out-of-system supply water 43B supplied bythe second compressor-condensate water line L₃₂ that is the water usedoutside the system.

Mode 1 of Using Compressor Condensate Water within System

In the following description, according to one or more embodiments, amode in which the compressor condensate water 43 that is separated atthe compressor-condensate water line L₃₀ from the condensate water drum44 is used as the in-system supply water 43A that is the water usedwithin the system will be explained.

As for the water used within the system, it needs to consider the waterbalance within the system of the CO₂ recovery system 10A. When thein-system supply water 43A is used, the second on-off valve V₂ and thethird to ninth on-off valves V₃ to V₉ are closed. Then, the in-systemsupply water 43A is made to connect to the washing-water circulationline L₇ that circulates through the washing unit 18B of the absorber 18via the end portion of the first compressor-condensate water line L₃₁.The in-system supply water 43A and the washing water 21 are then made tomerge so as to increase the percentage of water in the washing water 21and decrease the concentration of the absorption component in thewashing water 21.

When the compressor condensate water 43 is used as mechanical seal waterof various circulation pumps, by connecting the end portion of the firstcompressor-condensate water line L₃₁ to the rich solution pump 24 andthe lean solution pump 32 (*3), it is used as the mechanical seal water,for the pumps. Accordingly, this makes it unnecessary to supply the sealwater from the outside. Consequently, this can prevent the absorbentfrom being diluted by the water supply from the outside. In using thereflux water 31 in the pump equipment within the system, there is a riskof mixture of solid content such as soot dust when it is in anon-stationary operation condition in which a failure such as floodingoccurs at the top portion 20 c of the regenerator 20. However, becausethat risk of the compressor condensate water is low, the reduction inthe risk of damaging pump seal can be achieved.

Mode 2 of Using Compressor Condensate Water within System

Incidentally, as the CO₂ recovery system is continuously operated, theimpurities in the CO₂ absorbent increases. Thus, it needs to perform CO₂absorbent component regeneration operation (reclaimer operation) forremoving these deteriorated materials on a regular basis. This reclaimeroperation can be performed in conjunction with the CO₂ recoveryoperation. When performing this reclaimer operation, the compressorcondensate water 43 is used as reclaiming water.

FIGS. 2 to 5 are schematic diagrams illustrating the CO₂ recovery systemaccording to one or more embodiments. In the following description, withreference to FIGS. 2 to 5, a case in which the reclaimer operation isperformed will be explained.

Reclaimer Operation

As illustrated in FIG. 2, when using the in-system supply water 43A asthe reclaiming water of the reclaimer operation, by closing the first,the second, and the ninth on-off valves V₁, V₂, and V₉ and by openingthe third on-off valve V₃, the compressor condensate water 43 issupplied into the reclaimer 51 by the third compressor-condensate waterline L₃₃ as the reclaimer water. By opening the fourth on-off valve V₄and supplying the lean drawn liquid 17 a to the inside of the reclaimer51, by opening the fifth on-off valve V₅ and supplying the alkalineagent 52 a to the inside of the reclaimer 51 from the alkaline-agentsupply unit 52, by opening the sixth on-off valve V₆ and supplying thereflux water 31 a to the inside of the reclaimer 51, and by letting thesaturated water vapor 56 go through in the steam supply line L₁₅, thesupplied lean drawn liquid 17 a and the supply water (the compressorcondensate water 43 and the reflux water 31 a) are heated to, forexample, 120 to 150° C. by heat exchange in a non-contact manner. Then,the deteriorated materials that are non-volatile materials included inthe lean drawn liquid 17 a produce salt with the alkaline agent 52 a toseparate the salt from the absorption component, and the reclaimerresidue 54 is enriched.

When it is verified that the deteriorated materials in the CO₂ absorbentreached a certain concentration, by closing the fourth on-off valve V₄of the branch line L₁₀ and the fifth on-off valve V₅ of the alkalinesupply line L₁₁ and by stopping the supply of the lean drawn liquid 17 aand the alkaline agent 52 a, the reclaimer operation is ended.

Subsequently, a recovery operation that recovers the CO₂ absorptioncomponent from the enriched solution of the reclaimer 51 is performed.

This recovery operation is divided into an early-stage recoveryoperation (early stage of recovery) that recovers the CO₂ absorptioncomponent that constitutes the CO₂ absorbent, and into a late-stagerecovery operation (late stage of recovery) that performs finishingrecovery of the CO₂ absorption component that constitutes the CO₂absorbent.

FIG. 3 illustrates a case of an early stage of recovery of the recoveryoperation recovering the CO₂ absorption component, and FIG. 4illustrates a case of a late stage of recovery of the recovery operationrecovering the CO₂ absorption component.

Early Stage of Recovery

In the early stage of recovery, as the supply water to the reclaimer 51,the reflux water 31 a and the compressor condensate water 43 are used.

As illustrated in FIG. 3, when using the supply water 43A as thereclaiming water at the early stage of recovery of the reclaimeroperation, while keeping the first, the second, the fourth, and theninth on-off valves V₁, V₂, V₄, and V₉ closed and keeping the thirdon-off valve V₃ and the seventh on-off valve V₇ open, by supplying thein-system supply water 43A and the reflux water 31 a into the reclaimer51 as the compressor condensate water 43, the CO₂ absorption componentremaining in the residual liquid is recovered by making it entrained inthe recovery steam 53.

Late Stage of Recovery

In the late stage of recovery, as the supply water to the reclaimer 51,only the compressor condensate water 43 is used.

As illustrated in FIG. 4, when using the supply water as the reclaimingwater at the late stage of recovery of the reclaimer operation, byfurther closing the sixth on-off valve V₆ from the case of FIG. 3,stopping the supply of the reflux water 31 a, and supplying only thecompressor condensate water 43 into the reclaimer 51, the CO₂ absorptioncomponent of a very small amount remaining in the reclaimer residualwater is recovered by making it entrained in the recovery steam 53.

This is because the CO₂ absorption component remains (remaining amount:several wt %) in the reflux water 31 a, and when the CO₂ absorptioncomponent remains, due to vapor-liquid equilibrium, the vaporizationrate of the CO₂ absorption component entrained in the recovery steam 53is decreased.

Thus, in the late stage of recovery, by using the compressor condensatewater 43 for which the remaining CO₂ absorption component is of zero ora very small amount and that is compressed by the compressor, furtherimprovement in the recovery rate can be achieved.

Reclaimer Residue Discharge

After the recovery of CO₂ absorption component is finished, asillustrated in FIG. 5, by further closing the third on-off valve V₃ fromthe case of FIG. 4 and stopping the supply of the compressor condensatewater 43 to the reclaimer 51, and by opening the ninth on-off valve V₉of a fourth compressor condensate water line L₃₄ and supplying thecompressor condensate water 43 to the reflux water drum as the in-systemsupply water, the water balance is retained. Then, by opening the eighthon-off valve V₈ of the residue discharge line L₁₄ and operating aresidue discharge pump (not depicted), the reclaimer residue 54 isdischarged to the outside of the reclaimer 51.

FIG. 6 is a diagram illustrating the relation between the operatinghours (h) of absorption component recovery operation and the absorptioncomponent concentration (wt %) of residual water in the reclaimer.

As illustrated in FIG. 6, at the end time of the reclaimer operation,when the concentration of the absorption component is high as x₁, thereflux water 31 a and the compressor condensate water 43 are used incombination as the supply water to the reclaimer 51. At the latter halfof the early stage of recovery, the recovery efficiency of theabsorption component is reduced, and the curvature of the recovery curvebecomes gentle and reaches a low concentration x₂. When it reached thislow concentration x₂, by using only the compressor condensate water 43as the supply water to the reclaimer 51 and by further vaporizing theremaining CO₂ absorption component, the improvement in the recoveryefficiency of the CO₂ absorption component is achieved.

As a result of this, as compared with a conventional case in which thereflux water 31 a is used as the reclaiming water to the reclaimer 51,by using the compressor condensate water 43 for which the mix ratio ofthe absorption component is zero or very low, the improvement in therecovery efficiency of the CO₂ absorption component can be achieved.Thus, the effective use of the CO₂ absorption component remaining in theresidual water that has conventionally been discharged to the outside ofthe system as the reclaimer residue 54 and lost can be achieved.

Table 1 illustrates one example of an annual schedule of recovering CO₂in the flue gas by using the CO₂ recovery system. However, embodimentsof the present invention are not limited thereto.

In the present description, the CO₂ recovery system processes the fluegas at all times and is operated without stopping except for themaintenance and the like. Although the reclaimer processing depends alsoon the use frequency and the operating temperature of the CO₂ absorbent,it is implemented several times a year, for example. This implementationis conducted a predetermined number of times. Alternatively, byanalyzing the concentration of the deteriorated materials of the CO₂absorbent circulating in the circulatory system, if the result of theanalysis exceeds a prescribed value, a part of the CO₂ absorbentcirculating in the circulatory system is drawn out and supplied to thereclaimer and, while the deteriorated materials are separated andremoved from the CO₂ absorbent by adding the alkaline agent to thereclaimer, the CO₂ absorption component is returned to the circulatorysystem.

In the present description, conducting the reclaimer operation twice ayear as one example will be explained. In the annual schedule, for oneto four weeks in June and December, a part of the lean solution 17 isdrawn out to the reclaiming device 50 as the lean drawn liquid 17 a, andthe reclaimer operation is conducted.

Accordingly, except for this reclaimer operation, as illustrated in FIG.1, the compressor condensate water 43 that is the compressor condensatewater is used for the pump seal water as the in-system supply water 43A,for example. Then, when the reclaimer operation is conducted, asillustrated in FIGS. 2 to 5, the use as the pump seal water is stoppedand the compressor condensate water 43 is supplied into the reclaimer 51as the reclaiming water.

TABLE 1 Annual schedule 1 2 3 4 5 6 7 8 9 10 11 12 In-system ON--------> ON OFF ON --------> ON OFF supply water (43A) Reclaiming waterOFF --------> OFF ON OFF --------> OFF ON

FIG. 7 is a schematic diagram illustrating a CO₂ recovery systemaccording to one or more embodiments.

The constituent members identical to those of one or more embodimentsdescribed above are given identical reference signs and redundantdescriptions are omitted. As illustrated in FIG. 7, a CO₂ recoverysystem 10B according to one or more embodiments has a flash drum 60disposed on the third compressor-condensate water line L₃₃. This flashdrum 60 removes the CO₂ gas in the compressor condensate water 43, andit prevents supplying gas components in the reclaimer operation andimproves the recovery efficiency of the CO₂ absorption component.

FIG. 8 is a schematic diagram illustrating a CO₂ recovery systemaccording to one or more embodiments.

The constituent members identical to those of one or more embodimentsdescribed above are given identical reference signs and redundantdescriptions are omitted. As illustrated in FIG. 8, in a CO₂ recoverysystem 10C according to one or more embodiments, an inlet thermometer T₁that measures inlet gas temperature (t₁) in the gas supply line L₁ thatsupplies the flue gas 11 into the absorber 18 and an outlet thermometerT₂ that measures the outlet gas temperature (t₂) of the emission gasdischarged from a top portion 18 b of the absorber 18 are placed in theCO₂ recovery system 10A of one or more embodiments described above.

In the following description, according to one or more embodiments, themode in which the compressor condensate water 43 that is separated atthe compressor-condensate water line L₃₀ from the condensate water drum44 is used as the out-of-system supply water 43B that is the water usedoutside the system will be explained.

The out-of-system supply water 43B that is used outside the system isused in utilities of the system and is, for example, used as the supplywater for the water vapor of the saturated water vapor 27 supplied tothe reboiler 26 and as make-up water of the cooling water used in thecooling tower.

When it is used outside the system, it needs to make the amount ofdischarge smaller than the carried-in amount of water in the flue gas 11supplied into the absorber 18.

According to one or more embodiments, the outlet gas temperature (t₂) ofthe emission gas 11A discharged from the absorber is adjusted to belower than the inlet gas temperature (t₁) of the flue gas 11 suppliedinto the absorber 18, thereby keeping the water balance. In other words,because the inside of the system is a closed system, adjustment isneeded for the water discharged to the outside. Accordingly, when thecompressor condensate water 43 is used as the out-of-system supply water43B, the inlet thermometer (T₁) that measures the temperature of theflue gas 11 supplied into the absorber 18 and the outlet thermometer(T₂) that measures the temperature of the emission gas 11A dischargedfrom the CO₂ absorber are provided, and the operation is conducted bylowering the outlet gas temperature (t₂) of the emission gas 11A thanthe inlet gas temperature (t₁) of the flue gas 11, thereby making itpossible to ensure the water used outside the system.

In a bottom liquid-pool portion of the bottom portion 18 a of theabsorber 18, a liquid level meter L is installed, and the liquid levelis monitored. Accordingly, the liquid level in the bottom liquid-poolportion can be properly maintained. As a result, in the CO₂ recoverysystem, the reduction in the amount of water intake from the outside canbe achieved.

Table 2 illustrates the comparison between the case of using thecompressor condensate water 43 as the out-of-system supply water 43B andthe case of using it as the in-system supply water 43A.

When the compressor condensate water is used as the out-of-system supplywater 43B, the inlet thermometer (T₁) that measures the temperature ofthe flue gas 11 supplied into the absorber 18 and the outlet thermometer(T₂) that measures the temperature of the emission gas 11A dischargedfrom the absorber 18 are provided, and the operation is conducted bylowering the outlet gas temperature (t₂) of the emission gas 11A thanthe inlet gas temperature (t₁) of the flue gas 11. Accordingly, becausethe gas temperature of the emission gas 11A is lowered, the entrainedamount of the CO₂ absorbent entrained in the emission gas 11A is reducedand the reduction in emissions is achieved.

As one example, when the amount of water in the flue gas 11 suppliedinto the absorber 18 is 7.3 vol % and the inlet gas temperature (t₁) is40° C., assuming the outlet gas temperature (t₂) of the emission gas 11Adischarged from the top 18 b of the absorber 18 is 38° C., the water of0.8 vol % of the flue gas is to be obtained.

Meanwhile, in operating as the in-system supply water 43A so as toretain the water balance, when the amount of water in the flue gas 11supplied into the absorber 18 is 7.3 vol % and the inlet gas temperature(t₁) is 40° C., the outlet gas temperature (t₂) of the emission gas 11Adischarged from the top 18 b of the absorber 18 is set to 41° C. and ismaintained constant so that the water content of the emission gas 11A onthe outlet side becomes the water content in the flue gas 11 suppliedinto the absorber 18. The temperatures and the amounts of water,however, are examples, and should not be used to limit one or moreembodiments of the present invention.

TABLE 2 Out-of-system In-system supply supply water 43B water 43A(Washing (Reboiler steam water, reclaiming water, etc.) water, etc.)Absorber inlet 40° C. (Water 40° C. (Water gas temperature content: 7.3vol %) content: 7.3 vol %) (t₁) Outlet gas 38° C. (Water 41° C. (Watertemperature content: 6.5 vol %) content: 7.6 vol %) (t₂) Water reduction0.8 vol % —

As just described, when the compressor condensate water 43 is used asthe out-of-system supply water 43B, the discharge of the CO₂ absorptioncomponent entrained in the emission gas 11A discharged to the outsidecan be prevented and the reduction in emissions can be achieved.

In a case in which the operation to obtain the out-of-system supplywater 43B and the operation of reclaimer operation are used incombination, as illustrated in Table 3, in the present description,conducting the reclaimer operation twice a year as one example will beexplained. In the annual schedule, for one to three weeks in June andDecember, a part of the lean solution 17 is drawn out to the reclaimingdevice as the lean drawn liquid 17 a, and the reclaimer operation isconducted. Accordingly, except for this reclaimer operation, asillustrated in FIG. 8, the compressor condensate water 43 that is thecompressor condensate water is used as the out-of-system supply water43B, for example, as the supply water for the water vapor of thesaturated water vapor 27 supplied to the reboiler 26 and as the make-upwater of the cooling water used in the cooling tower.

TABLE 3 Annual schedule 1 2 3 4 5 6 7 8 9 10 11 12 Out-of-system ON--------> ON OFF ON --------> ON OFF supply water (43B) Reclaiming waterOFF --------> OFF ON OFF --------> OFF ON

Then, when the reclaimer operation is conducted, as illustrated in FIGS.2 to 5, the use as the pump seal water is stopped and the compressorcondensate water 43 is supplied into the reclaimer 51 as the reclaimingwater. According to one or more embodiments, because it is used as theout-of-system supply water 43B, the discharge of the CO₂ absorptioncomponent entrained in the emission gas 11A discharged to the outsidecan be prevented and the reduction in emissions can be achieved.

In addition, as the out-of-system supply water 43B, it can also be used,for example, as the substitute of the make-up water of the utilityfacilities that are peripherals, or as a part thereof. At this time, aremoval device such as an ion exchange resin is installed, for example.As a result, the CO₂ absorption component of an infinitesimal amountincluded in the compressor condensate water 43 can be removed.

Although the disclosure has been described with respect to only alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that various other embodiments maybe devised without departing from the scope of the present invention.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A CO₂ recovery system comprising: a CO₂ absorber that: transportsflue gas comprising CO₂ into contact with a CO₂ absorbent to remove theCO₂ from the flue gas, and discharges a rich solution that has absorbedthe CO₂; an absorbent regenerator that separates the CO₂ from the richsolution to regenerate the CO₂ absorbent as a lean solution; a gasdischarge line where a CO₂ entrained gas, discharged from a top portionof the absorbent regenerator, is discharged; a reflux water drum,disposed in the gas discharge line, that produces reflux water byseparating the CO₂ and water from the CO₂ entrained gas; aseparation-gas discharge line where the CO₂ separated by the refluxwater drum is discharged; a compressor disposed in the separation-gasdischarge line that compresses the separated CO₂ gas; a condensate waterdrum, disposed in the separation-gas discharge line, that producescompressor condensate water by separating the water from the compressedCO₂ gas; and a compressor-condensate water line, connected to thecondensate water drum, that supplies the compressor condensate water asin-system supply water or out-of-system supply water.
 2. The CO₂recovery system according to claim 1, wherein the in-system supply wateris at least one of washing water for a washing unit of the CO₂ absorber,pump seal water, and reclaiming water for a reclaiming device.
 3. TheCO₂ recovery system according to claim 1, further comprising: areclaiming device that regenerates the CO₂ absorbent, wherein: thereclaiming device is connected to an end portion of thecompressor-condensate water line and includes: a branch line that drawsa part of the lean solution as lead drawn liquid, a reclaimer that takesin and reserves the lean drawn liquid, an alkaline-agent supply unitthat supplies an alkaline agent into the reclaimer via an alkalinesupply line, a reflux-water supply line that supplies the reflux waterinto the reclaimer, a recovery-steam discharge line that suppliesrecovery steam discharged from the reclaimer to a bottom portion side ofthe absorbent regenerator, and a heating unit that heats an inside ofthe reclaimer.
 4. The CO₂ recovery system according to claim 3, whereinthe reclaiming device is subjected to, after regeneration of the CO₂absorbent is completed: an early-stage recovery operation that: closesthe branch line and stops supplying the lean drawn liquid into thereclaimer, and recovers a CO₂ absorption component that forms the CO₂absorbent, and a late-stage recovery operation that: closes thereflux-water supply line to stop supplying the reflux water into thereclaimer, and performs finishing recovery of the CO₂ absorptioncomponent using the compressor condensate water.
 5. The CO₂ recoverysystem according to claim 3, further comprising a flash drum thatseparates gas from the compressor condensate water to be supplied intothe reclaiming device.
 6. The CO₂ recovery system according to claim 1,further comprising: an inlet thermometer that measures a temperature ofthe flue gas to be supplied to the CO₂ absorber; an outlet thermometerthat measures a temperature of emission gas discharged from the CO₂absorber, wherein the CO₂ recovery system uses the compressor condensatewater as the out-of-system supply water by regulating the temperature ofthe emission gas to be lower than the temperature of the flue gas.
 7. Amethod of circulating and reusing with a CO₂ absorber a CO₂ absorbentwith the CO₂ removed by an absorbent regenerator, the CO₂ absorberbrings flue gas comprising the CO₂ into contact with the CO₂ absorbentto remove the CO₂ and discharges a rich solution that has absorbed theCO₂, the absorbent regenerator separates the CO₂ from the rich solutionto regenerate the CO₂ absorbent as a lean solution, the methodcomprising: separating, by a reflux water drum, the CO₂ and water from aCO₂ entrained gas discharged from a top portion of the absorbentregenerator to produce reflux water; compressing the CO₂ separated bythe reflux water drum; and separating water from the compressed CO₂ gasto form compressor condensate water, wherein the compressor condensatewater is used as in-system supply water or out-of-system supply water.8. The method of recovering CO₂ according to claim 7, furthercomprising: in conducting reclaimer operation, using a reclaiming devicecomprising a reclaimer, of the CO₂ absorbent by using the reflux waterand the compressor condensate water in a reclaiming device afterregeneration of the CO₂ absorbent is completed: executing an early-stagerecovery operation that: stops supplying a lean drawn liquid that ispart of the lean solution into the reclaimer, and recovers a CO₂absorption component that forms the CO₂ absorbent, and executing alate-stage recovery operation that: stops supplying the reflux waterinto the reclaimer, and performs finishing recovery of the CO₂absorption component using the compressor condensate water.